1. S. Weinberg,Gravitation and Cosmology (Wiley, New York, 1972).
2. A. Einstein, The Foundation of the General Theory of Relativity, in H. A. Lorentzet al., eds.,The Principle of Relativity (Dover, New York, 1952).
3. M. M. Hatalkar,Phys. Rev. 94, 1472 (1954).
4. R. Utiyama,Phys. Rev. 101, 1597 (1956).
5. D. R. Brill and J. M. Cohen,J. Math. Phys. 7, 238 (1966).